Process for recovery of copper from copper-bearing material using pressure leaching, direct electrowinning and solvent/solution extraction

ABSTRACT

The present invention relates generally to a process for recovering copper and/or other metal values from a metal-bearing ore, concentrate, or other metal-bearing material using pressure leaching and direct electrowinning. More particularly, the present invention relates to a substantially acid-autogenous process for recovering copper from chalcopyrite-containing ore using pressure leaching and direct electrowinning in combination with a leaching, solvent/solution extraction and electrowinning operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/623,453; entitled “Process for Recovery ofCopper From Copper-Bearing Material Using Pressure Leaching, DirectElectrowinning and Solvent/Solution Extraction” filed Oct. 29, 2004.

FIELD OF INVENTION

The present invention relates generally to a process for recoveringcopper and other metal values from a metal-bearing material usingpressure leaching and direct electrowinning. More particularly, thepresent invention relates to a process using fine grinding, pressureleaching, and direct electrowinning in combination with solvent/solutionextraction to recover metal from the metal-bearing material.

BACKGROUND OF INVENTION

Hydrometallurgical treatment of copper-containing materials, such ascopper ores, copper-bearing concentrates, and other copper-bearingmaterials, has been well established for many years. However, aneffective and efficient method to recover copper from copper-containingmaterials, especially copper from copper sulfides such as chalcopyriteand chalcocite, that enables high copper recovery to be achieved at areduced cost over conventional processing techniques would beadvantageous.

SUMMARY OF INVENTION

In general, according to various aspects of the present invention, aprocess for recovering copper and other metal values from ametal-bearing material includes various physical conditioning, reaction,and recovery processes. For example, in accordance with the variousembodiments of the present invention, fine grinding of the metal-bearingmaterial prior to reactive processing, such as by medium or hightemperature (as will be defined hereinbelow) pressure leaching, resultsin enhanced metal value recovery and various other advantages over priorart metal recovery processes. Moreover, proper conditioning enablesdirect electrowinning of copper from a pressure leaching product streamwithout the use of an intermediate solvent/solution extraction step.Further, at least a portion of the impurities and excess acid in theprocess stream are removed through the use of a lean electrolyte bleedstream from electrowinning that may be further processed in asolvent/solution extraction and electrowinning operation.

In accordance with one exemplary embodiment of the present invention, aprocess for recovering copper from a copper-bearing material includesthe steps of: (i) providing a feed stream containing copper-bearingmaterial; (ii) subjecting the copper-bearing feed stream to controlledfine grinding; (iii) pressure leaching the copper-bearing feed stream toyield a copper-containing solution; (iv) recovering cathode copper fromthe copper-containing solution; (v) treating at least a portion of alean electrolyte stream from the copper recovery step in asolvent/solution extraction and electrowinning operation; and (vi)recycling at least a portion of the lean electrolyte stream to thepressure leaching step to provide some or all of the acid requirement ofthe pressure leaching operation.

In accordance with another exemplary embodiment, a process forrecovering copper includes the steps of: (i) providing a feed stream ofcopper-containing material; (ii) subjecting the copper containing feedstream to atmospheric leaching or pressure leaching to yield acopper-containing solution; (iii) conditioning the copper-containingsolution through one or more chemical or physical conditioning steps;and (iv) electrowinning copper directly from the copper-containingsolution, without subjecting the copper-containing solution to solventextraction. As used herein, the term “pressure leaching” shall refer toa metal recovery process in which material is contacted with an acidicsolution and oxygen under conditions of elevated temperature andpressure.

In accordance with another aspect of an exemplary embodiment of theinvention, a bleed stream of lean electrolyte from the electrowinningstage advantageously removes at least a portion of the excess acid fromthe metal recovery process and also impurities contained therein, thuspreventing such impurities from accumulating to deleterious levels inthe process and negatively impacting production efficiencies and product(e.g., copper cathode) quality. In accordance with one embodiment of theinvention, excess acid removed in the lean electrolyte bleed stream maybe utilized in other copper extraction processes, or the acid may beconsumed by using suitable materials, such as, for example, low gradecopper ore, mining waste products, and/or other rock products containingacid neutralizing minerals, such as limestone, dolomite, feldspar, andthe like.

In accordance with another aspect of an exemplary embodiment of theinvention, acid generated in the pressure leaching and electrowinningsteps is recycled to the pressure leaching step and provides acid neededfor effective leaching of copper. In this way, the use of recycledacid-containing solution, rather than concentrated sulfuric acid, iseconomically advantageous.

These and other advantages of a process according to various aspects ofthe present invention will be apparent to those skilled in the art uponreading and understanding the following detailed description withreference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present invention is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present invention, however, may bestbe obtained by referring to the detailed description when considered inconnection with the drawing figures, wherein like numerals denote likeelements and wherein:

FIG. 1 illustrates a flow diagram of a copper recovery process inaccordance with one exemplary embodiment of the present invention;

FIG. 1A illustrates a flow diagram of an aspect of an exemplaryembodiment of the present invention;

FIG. 2 illustrates a flow diagram of various aspects of a copperrecovery process in accordance with an exemplary embodiment of thepresent invention; and,

FIG. 3 is a graph plotting copper concentration in the pressure leachingresidue as a function of acid addition in accordance with variousaspects of an exemplary embodiment of the invention.

DETAILED DESCRIPTION

Various embodiments of the present invention exhibit significantadvancements over prior art processes, particularly with regard tocopper recovery and process efficiency. In accordance with an exemplaryembodiment of the present invention, a process for recovering copperfrom a copper-bearing material includes the steps of: (i) providing afeed stream containing copper-bearing material; (ii) subjecting at leasta portion of the copper-bearing feed stream to controlled fine grinding;(iii) pressure leaching the copper-bearing feed stream to yield acopper-containing solution; (iv) recovering cathode copper from thecopper-containing solution by electrowinning; (v) treating at least aportion of a lean electrolyte stream from the copper recovery step bysolvent/solution extraction followed by an electrowinning operation; and(vi) recycling at least a portion of the lean electrolyte stream to thepressure leaching step.

Various embodiments of the present invention exhibit significantadvancements over prior art processes, particularly with regard tocopper recovery and process efficiency. In accordance with anotherexemplary embodiment of the present invention, a process for recoveringcopper from a metal-bearing material includes the steps of: (i)providing a feed stream containing copper-bearing material; (ii)subjecting at least a portion of the copper-bearing feed stream tocontrolled fine grinding; (iii) pressure leaching the copper-bearingfeed stream to yield a copper-containing solution; (iv) recoveringcathode copper from the copper-containing solution by electrowinning;(v) treating at least a portion of a lean electrolyte stream from thecopper recovery step by solvent/solution extraction followed by anelectrowinning operation; and (vi) optionally, recycling at least aportion of the lean electrolyte stream to the pressure leaching step.

In accordance with another exemplary embodiment, a process forrecovering copper includes the steps of: (i) providing a feed stream ofcopper-containing material; (ii) subjecting the copper containing feedstream to atmospheric leaching or pressure leaching to yield acopper-containing solution; (iii) conditioning the copper-containingsolution through one or more chemical or physical conditioning steps;and (iv) electrowinning copper directly from the copper-containingsolution, without subjecting the copper-containing solution to solventextraction. As used herein, the term “pressure leaching” shall refer toa metal recovery process in which material is contacted with an acidicsolution and oxygen under conditions of elevated temperature andpressure.

Existing copper recovery processes that utilize conventional atmosphericor pressure leaching, solvent/solution extraction and electrowinningprocess steps may, in many instances, be easily retrofitted to exploitthe many commercial benefits the present invention provides. Medium orhigh temperature pressure leaching processes for chalcopyrite aregenerally thought of as those processes operating at temperatures fromabout 120° C. to about 190° C. or up to 220° C.

Referring first to FIG. 1, in accordance with various aspects of thepresent invention, a metal-bearing material 101 is provided forprocessing. Metal-bearing material 101 may be an ore, a concentrate, aprecipitate, or any other material from which copper and/or other metalvalues may be recovered. Metal values such as, for example, copper,gold, silver, platinum group metals, nickel, cobalt, molybdenum,rhenium, uranium, rare earth metals, and the like, may be recovered frommetal-bearing materials in accordance with various embodiments of thepresent invention. The various aspects and embodiments of the presentinvention, however, prove especially advantageous in connection with therecovery of copper from copper-bearing sulfide ores, such as, forexample, ores and/or concentrates and/or precipitates containingchalcopyrite (CuFeS₂), chalcocite (Cu₂S), bornite (Cu₅FeS₄), covellite(CuS), enargite (Cu₃AsS₄), digenite (Cu₉S₅) and mixtures thereof. Thus,metal-bearing material 101 preferably is a copper ore, concentrate orprecipitate, and, more preferably, is a copper-bearing sulfide ore,concentrate or precipitate. In accordance with yet another aspect of thepresent invention, metal-bearing material 101 may comprise a concentratethat is not a flotation concentrate or precipitate thereof. For ease ofdiscussion, the description of various exemplary embodiments of thepresent invention hereinbelow generally focuses on the recovery ofdesired metal values from chalcopyrite-containing ore or concentrate,however, any suitable metal bearing material may be utilized.

In accordance with an exemplary embodiment of the present invention,copper is the metal to be recovered from a metal-bearing material, suchas a copper sulfide concentrate. One aspect of this exemplary embodimentinvolves use of a copper sulfide concentrate produced by frothflotation. In preparation for froth flotation, the metal-bearingmaterial feed stream is ground to a particle size suitable to liberatemineral-bearing particles from gangue materials. However, as notedabove, other concentrates may also be utilized.

Metal-bearing material 101 may be prepared for metal recovery processingin any manner that enables the conditions of metal-bearing material 101to be suitable for the chosen processing method, as such conditions mayaffect the overall effectiveness and efficiency of processingoperations. For example, feed stream conditions such as particle size,composition, and component concentrations can affect the overalleffectiveness and efficiency of downstream processing operations, suchas, for example, atmospheric leaching or pressure leaching. Desiredcomposition and component concentration parameters can be achievedthrough a variety of chemical and/or physical processing stages, thechoice of which will depend upon the operating parameters of the chosenprocessing scheme, equipment cost and material specifications.

It is generally known that hydrometallurgical processes, particularlypressure leaching processes, are sensitive to particle size. Thus, it iscommon practice in the area of extractive hydrometallurgy to finelydivide, grind, and/or mill mineral species to reduce particle sizesprior to processing by pressure leaching. It generally has beenappreciated that reducing the particle size of a mineral species, suchas, for example, a copper sulfide, enables pressure leaching under lessextreme conditions of pressure and temperature to achieve the same metalextraction as achieved under conditions of higher temperature andpressure. The particle size distribution can also affect other leachingconditions, such as, for example, acid concentration and oxygenoverpressure.

A variety of acceptable techniques and devices for reducing the particlesize of the metal-bearing material are currently available, such as ballmills, tower mills, superfine grinding mills, attrition mills, stirredmills, horizontal mills and the like, and additional techniques maylater be developed that may achieve the desired result of increasing thesurface area of the material to be processed.

For example, metal-bearing material 101 may be prepared for metalrecovery processing by controlled fine grinding. Preferably, it isadvantageous not only to reduce the size of the metal-bearing materialparticles in the process stream, but also to ensure that the weightproportion of the coarsest particles is minimized. Significantadvantages in processing efficiency and copper recovery are achievableby enabling substantially all particles to react substantiallycompletely.

In accordance with one embodiment of the present invention, and withreference to FIG. 1 and FIG. 1A, while controlled fine grinding mayutilize any now known or hereafter devised methodology, in general,grinding step 1010 includes controlled, fine grinding step 1010A,optional size classification step 1010B and solid liquid separation step1010C. Preferably, grinding in accordance with this aspect of thepresent invention proceeds in a staged or closed-circuit manner. Thatis, preferably the coarsest particles of metal-bearing material 101 aresuitably ground to the desired level, while particles already at orbelow the desired level are subjected to little or no additionalgrinding. As such, cost savings can be obtained in connection withgrinding operations, while at the same time limiting the size and weightproportion of the coarsest particles. However, open-circuit grinding mayalso produce an acceptable product.

With continued reference to FIG. 1A, preferably cyclone technology, suchas, for example, use of cyclones, or mini-cyclones, is utilized tofacilitate size classification step 1010B by separating relativelycoarse materials from relatively fine materials. That is, after material101 is ground in controlled fine grinding step 1010A, the coarsematerial 10 is suitably separated from the fine material 12, such thatcoarse material 10 may be further ground, as shown in FIG. 1A in stream11. Similarly, in accordance with one aspect of an exemplary embodimentof the invention wherein the chosen grinding method and apparatusutilize a liquid processing agent (such as, for example, process water)to facilitate grinding in super-fine grinding stage 1010, an optionalsolid-liquid separation stage 1010C may be utilized to remove excessprocessing liquid 13 from the process stream 102 prior to pressureleaching, and preferably recycle excess process liquid 13 to super-finegrinding stage 1010A for reuse. Depending upon the configuration of thegrinding apparatus, solid-liquid separation stage 1010C may or may notbe required. If, however, process liquid is added to copper-containingmaterial 101 prior to or during super-fine grinding 1010, it may bedesirable to remove at least a portion of the added process liquid fromcopper-containing material stream 102 prior to pressure leachingoperation 1030 to optimize slurry density.

Grinding step 1010 preferably results in material 110 being finelyground, such that the particle size of the material being processed isreduced such that substantially all of the particles are small enough toreact substantially completely during pressure leaching.

Various particle sizes and particle size distributions may beadvantageously employed in accordance with various aspects of thepresent invention. For example, in accordance with one aspect of thepresent invention grinding step 1010 results in material 110 beingfinely ground to a P80 on the order of less than about 25 microns, andpreferably on the order of a P80 between about 13 and about 20 microns.

In accordance with another aspect of the present invention, thecopper-containing material has a P80 of less than about 250 microns,preferably a P80 from about 75 to about 150 microns, and more preferablya P80 on the order of from about 5 to about 75 microns.

In accordance with yet another aspect of the present invention, aparticle size distribution of approximately 98 percent passing about 25microns is preferable, and more preferably, the metal-bearing materialstream has a particle size distribution of approximately 98 percentpassing from about 10 to about 23 microns, and optimally from about 13to about 15 microns.

While, as noted, grinding step 1010 may be conducted in any manner,satisfactory controlled fine grinding may be achieved using a finegrinding apparatus, such as, for example, a stirred horizontal shaftmill with baffles or a vertically stirred mill without baffles. Suchexemplary apparatus include the Isamill developed jointly by Mount IsaMines (MIM), Australia, and Netzsch Feinmahitechnik, Germany and the SMDor Detritor mill, manufactured by Metso Minerals, Finland. Preferably,if a horizontal mill is utilized, the grinding medium would be 1.2/2.4mm or 2.4/4.8 mm Colorado sand, available from Oglebay Norton IndustrialSands Inc., Colorado Springs, Colo. However, any grinding medium thatenables the desired particle size distribution to be achieved may beused, the type and size of which may be dependent upon the applicationchosen, the product size desired, grinding apparatus manufacturer'sspecifications, and the like. Exemplary media include, for example,sand, silica, metal beads, ceramic beads, and ceramic balls.

The comminuted metal-bearing material may be combined with a liquidprior to entering reactive processing stage 1030 (describedhereinbelow). Preferably, if employed, the liquid comprises water, butany suitable liquid may be employed, such as, for example, raffinate,pregnant leach solution, or lean electrolyte. For example, a portion ofthe lean electrolyte from the direct electrowinning process (forexample, stream 119) may be combined with comminuted metal-bearingmaterial to form metal-bearing material stream 103 for delivery toreactive processing stage 1030. In this way, acid is recycled to theprocess stream such that it helps to satisfy the acid demand of reactiveprocessing stage 1030.

The combination of a liquid with the metal-bearing material can beaccomplished using any one or more of a variety of techniques andapparatus, such as, for example, in-line blending or using a mixing tankor other suitable vessel. In accordance with an exemplary aspect of anembodiment of the invention, the concentration of solid metal-bearingmaterial in the material stream (i.e., the slurry density) is on theorder of less than about fifty (50) percent by weight of the stream, andpreferably about forty (40) percent by weight of the stream. Otherslurry densities that are suitable for transport and subsequentprocessing may, however, be used.

In accordance with one aspect of the present invention, it is desirableto separate the copper in a recycled stream of lean electrolyte fromelectrowinning from the acid, and also to reduce the amount ofcontaminants in the portion of the stream to be subjected to the metalrecovery process. In such a separation process, the acid that is removedfrom the recycled lean electrolyte stream may be rejected from theprocess circuit, taking with it at least a portion of the metalcontaminants and other soluble impurities from the copper-containingfeed stream and the recycled lean electrolyte stream. Any number ofconventional or hereafter devised separation processes and techniquesmay be useful to achieve the separation of copper from acid in the feedstream. For example, separation processes and/or techniques such asprecipitation, low temperature pressure leaching, acid solventextraction/ion exchange, membrane separation, cementation, pressurereduction, sulfiding, and/or the use of liberator cells may be usefulfor this purpose.

The separation aspect of a preferred embodiment of the inventioncontributes to providing a resultant acid stream that contains arelatively small fraction of copper, which can be used for leaching, pHcontrol, or other applications. Moreover, utilization of a separationprocess in accordance with this aspect of the invention may beparticularly advantageous in that it may enable contaminants from theunrefined copper-containing material stream to be removed from thecopper-containing material stream and incorporated into the resultantacid stream. Because the resultant acid stream is preferably removedfrom the metal recovery process altogether and utilized in remoteoperations, disposed of, or neutralized, the contaminants containedtherein are likewise removed from the metal recovery process and arethus prevented from accumulating in the process stream. This may be asignificant advantage in that such contaminants, particularly metalcontaminants, typically have a deleterious effect on the effectivenessand efficiency of the desired metal recovery process. For example, metalcontaminants and other impurities in the process stream, if notcarefully controlled and/or minimized, can contribute to diminishedphysical and/or chemical properties in the cathode copper produced byelectrowinning, and can thus degrade the copper product and diminish itseconomic value.

Referring again to FIG. 1, in accordance with one aspect of a preferredembodiment of the invention, copper-containing material stream 101 issubjected to a separation, such as, for example, a precipitation step,which, in this exemplary process, serves to precipitate solubilizedcopper from a recycled lean electrolyte stream onto the surfaces ofsolid particles in the copper-containing material stream. As discussedin detail above, this aspect offers an important advantage in that itenables recovery of copper from a lean electrolyte stream that otherwisemay have been lost or would have required additional processing torecover, potentially resulting in significant economic benefits.

In this preferred aspect of the invention, the precipitation stepinvolves the copper-containing material stream being combined with asulfur dioxide (SO₂) stream 109 and a lean electrolyte stream 108 in asuitable processing vessel. For example, in the embodiment illustratedin FIG. 1, lean electrolyte stream 108 may comprise a recycled acidiccopper sulfate stream generated during an electrowinning operation.Other streams, however, preferably copper-rich streams, may also beused. Preferably, precipitation is carried out such that the copper fromthe lean electrolyte precipitates, at least in part, onto the surface ofunreacted copper-containing material particles within stream 101 in theform of copper sulfides, such as, for example, CuS.

In accordance with a preferred aspect of the invention, copperseparation stage 1010 is carried out at a slightly elevated temperature,such as from about 70° C. to about 180° C., preferably from about 80° C.to about 100° C., and most preferably at a temperature of about 90° C.Heating, if necessary, can be effectuated through any conventionalmeans, such as electric heating coils, a heat blanket, process fluidheat exchange, and other ways now known or later developed. In anexemplary process, steam may be generated in other process areas, andmay be directed to the processing vessel in copper separation stage 1010to provide the heat desired to enhance the precipitation process. Theresidence time for the copper precipitation process can vary, dependingon factors such as the operating temperature of the processing vesseland the composition of the copper-containing material, but typicallyranges from about thirty (30) minutes to about 6 hours. Preferably,conditions are selected such that significant amounts of copper areprecipitated. For example, precipitation rates on the order of about 98%precipitation of copper have been achieved in processing vesselsmaintained at about 90° C. for about 4 hours.

Referring to FIG. 1, after metal-bearing material stream 103 has beensuitably prepared for processing by controlled fine grinding, liquidaddition, and, optionally, other physical and/or chemical conditioningprocesses, it is subjected to a reactive processing step 1030, forexample, metal extraction via pressure leaching. In accordance with oneembodiment of the present invention, reactive processing step 1030comprises pressure leaching. Preferably, reactive processing step 1030is a medium temperature pressure leaching process operating at atemperature in the range of about 140° C. to about 230° C. In accordancewith one embodiment, pressure leaching preferably is conducted in therange of about 140° C. to about 180° C., and generally, above about 160°C., and more preferably in the range of about 160° C. to about 170° C.In accordance with another embodiment, pressure leaching is conducted attemperatures above 180° C., and preferably in the range of about 180° toabout 220° C., and more preferably in the range of about 190° C. toabout 210° C.

In accordance with various aspects of the present invention, the optimumtemperature range selected for operation will tend to maximize theextraction of copper and other metals, optimize production of elementalsulfur (S°), minimize fresh acid consumption, and thereby minimizemake-up acid requirements. Acid and sulfur are made from oxidation ofsulfide according to the following reactions:4CuFeS₂+17O₂+4H₂O→2Fe₂O₃+4Cu²⁺+8H⁺+8SO₄ ²⁻  (1)4CuFeS₂+8H⁺+5O₂→2Fe₂O₃+4Cu²⁺+8S°+4H₂O   (2)

Preferably, in accordance with the present invention, the conditions(temperature, acid concentration) for the pressure leaching step aresuitably selected to achieve an advantageous balance between reactions(1) and (2), but tending to reduce or eliminate fresh make-up acidconsumption and thus the costs associated with acid make-up, but withoutsacrificing copper extraction to any significant extent.

The amount of acid introduced into the pressure leaching vessel variesdepending upon the reaction parameters, particularly, reactiontemperature, iron dissolution, copper extraction, and sulfide oxidation.Make-up acid may be introduced into the pressure leaching vessel in theform of fresh acid or recycled acid from the same recovery process oranother process. In certain cases, make-up acid is introduced on theorder of from about 300 to about 650 kilograms per tonne of concentrate,or less; however, lower make-up acid is required at higher temperatures.

The present inventors have discovered that operating parameters of themetal recovery process of the present invention may be optimized toachieve any number of economic, processability, or productionobjectives. Generally speaking, for example, at a fixed acid recyclerate, as the temperature in the pressure leaching stage is increased,more oxygen is consumed, more acid is produced, and less elementalsulfur is produced. Iron dissolution can be controlled at highertemperatures by reducing recycled acid from stream 119. Moreover,keeping all other parameters constant, as the temperature in thepressure leaching stage is increased, copper recovery may be maximized.Thus, at increased temperatures and a fixed acid recycle rate, more acidmay be produced during pressure leaching (i.e., excess acid that must beconsumed) and more oxygen may be consumed, but higher copper recoverymay be possible. At lower temperatures (e.g., 140-150° C.), the pressureleaching operation may require more recycled acid and copper recoverymay be reduced, but less oxygen is demanded and the cost of consumingexcess acid is reduced. Within a temperature range of from about 150° C.to about 170° C., however, an acid autogenous process may bepossible—that is, the pressure leaching operation may produceapproximately the acid that it requires. As such, it may be possible toreduce or eliminate the costs of make-up acid and acid attenuation whileachieving acceptable copper recovery and moderate oxygen consumption.However, in accordance with other embodiments of the present inventionhigher temperatures may be utilized. For example, on the order of about200° C. to about 210° C. may tend to enhance copper recovery.

It should be noted that any of the above scenarios may be desirableunder certain circumstances. That is, extrinsic factors—such as powerand raw material costs or the market price of copper and/or otherrecoverable metal values—may dictate whether it would be mosteconomically desirable to operate the pressure leaching operation atlower temperatures (e.g., if cost of acid attenuation is higher thanacid purchase, if oxygen is expensive, if power costs are high, and/orif copper price is low), or higher temperatures (e.g., if cost of acidattenuation is lower than acid purchase, if acid can be usedbeneficially elsewhere, if oxygen is inexpensive, if power costs arelow, and/or if copper price is high).

At medium temperature conditions (i.e., between about 140° C. and about180° C.), ferric ion in solution will hydrolyze in the pressure leachingvessel to form hematite and sulfuric acid by the following reaction:Fe₂(SO₄)₃ (aq)+3H₂O (I)→Fe₂O₃ (s)+3H₂SO₄ (aq)

As the iron concentration in the pressure leaching vessel increases, theiron concentration in the rich electrolyte stream (i.e., the pressureleaching discharge liquor) also increases. Increasing iron in thepressure leaching discharge generally results in an undesirable drop inthe current efficiency in subsequent electrowinning operations.Decreased current efficiency in electrowinning results in increasedoperating costs per unit of copper recovered through electrowinning.

The total acid addition (free acid in solution plus iron-equivalent acidcontent of solution) to the pressure leaching step is preferablycontrolled to optimize the copper extraction (as indicated by the copperin the residue) and iron in the rich electrolyte for directelectrowinning. In general, the residue copper content decreases withincreasing total acid addition to the pressure leaching step, while theamount of iron in solution tends to increase with increasing total acidaddition.

In accordance with an exemplary embodiment of the invention, a processfor recovering copper from copper-bearing material is operated such thatthe highest total acid addition to the pressure leaching vessel isutilized above which there is little or no additional benefit to theresidue copper content. In accordance with one embodiment of theinvention, the total acid addition to the pressure leaching vessel is inthe range of from about 400 to about 500 kg/tonne.

Turning again to FIG. 1, reactive processing step 1030 may occur in anypressure leaching vessel suitably designed to contain the pressureleaching mixture at the desired temperature and pressure conditions forthe requisite pressure leaching residence time. In accordance with oneaspect of an exemplary embodiment of the invention, the pressureleaching vessel used in processing step 1030 is an agitated,multi-compartment horizontal pressure leaching vessel. However, itshould be appreciated that any pressure leaching vessel that suitablypermits metal-bearing material stream 103 to be prepared for copperrecovery may be utilized within the scope of the present invention.

During reactive processing step 1030, copper and/or other metal valuesmay be solubilized or otherwise liberated in preparation for laterrecovery processes. Any substance that assists in solubilizing—and thusliberating—the metal value, and thus releasing the metal value from ametal-bearing material, may be used. For example, where copper is themetal being recovered, an acid, such as sulfuric acid, may be contactedwith the copper-bearing material such that the copper may be liberatedfor later recovery steps. However, it should be appreciated that anysuitable method of liberating metal values in preparation for latermetal recovery steps may be utilized within the scope of this invention.

Any agent capable of assisting in the solubilization of the copper, suchas, for example, sulfuric acid, may be provided during the reactiveprocessing step 1030, such as, for example, medium temperature pressureleaching, in a number of ways. For example, such acid may be provided ina cooling stream provided by the recycle of lean electrolyte 119 fromelectrowinning stage 1070. However, it should be appreciated that anymethod of providing for the solubilization of copper is within the scopeof the present invention. The amount of acid added during pressureleaching preferably is balanced according to the acid needed to optimizecopper extraction and, if desired, to achieve a substantially acidautogenous process.

In accordance with various aspects of the present invention, thepressure leaching process occurs in a manner suitably designed topromote substantially complete solubilization of the copper, it may bedesirable to introduce additional materials to enhance the pressureleaching process. In accordance with one aspect of the presentinvention, during pressure leaching in a pressure leaching vessel,sufficient oxygen 105 is injected into the vessel to maintain an oxygenpartial pressure from about 50 to about 250 psig, preferably from about75 to about 220 psig, and most preferably from about 150 to about 200psig. Furthermore, due to the nature of medium temperature pressureleaching, the total operating pressure (including oxygen partialpressure) in the pressure leaching vessel is generally superatmospheric,preferably from about 100 to about 750 psig, more preferably from about250 to about 400 psig, and most preferably from about 270 to about 350psig.

The residence time for pressure leaching can vary, depending on factorssuch as, for example, the characteristics of the copper-bearing materialand the operating pressure and temperature of the pressure leachingvessel. In one aspect of an exemplary embodiment of the invention, theresidence time for the medium temperature pressure leaching ofchalcopyrite ranges from about 30 to about 180 minutes, more preferablyfrom about 60 to about 150 minutes, and most preferably on the order ofabout 80 to about 120 minutes.

Control of the pressure leaching process, including control of thetemperature in the pressure leaching vessel, may be accomplished by anyconventional or hereafter devised method. For example, with respect totemperature control, preferably the pressure leaching vessel includes afeedback temperature control feature. For example, in accordance withone aspect of the invention, the temperature of the pressure leachingvessel is maintained at a temperature in the range of about 140° C. toabout 180° C. and more preferably in the range of about 150° C. to about175° C. In accordance with another aspect of the invention, thetemperature may be suitably selected to be above about 180° C., and morepreferably in the range of about 180° C. to about 220° C. As such, awide range of temperatures may be useful in connection with the variousaspects of the present invention.

Due to the exothermic nature of pressure leaching of metal sulfides, theheat generated by medium temperature pressure leaching is generally morethan that needed to heat the feed stream to the desired operatingtemperature. Thus, in order to maintain preferable pressure leachingtemperature, a cooling liquid 106 may be introduced into the pressureleaching vessel during pressure leaching. In accordance with one aspectof an embodiment of the present invention, cooling liquid 106 ispreferably contacted with the feed stream in the pressure leachingvessel during pressure leaching. Cooling liquid 106 may comprise make-upwater, but can be any suitable cooling fluid from within the process orfrom an outside source, such as recycled liquid from the product slurry,lean electrolyte, or a mixture of cooling fluids. Cooling liquid 106 maybe introduced into the pressure leaching vessel through the same inletas feed slurry, or alternatively in any manner that effectuates coolingof the feed slurry. The amount of cooling liquid 106 added to the feedslurry during pressure leaching may vary, depending on the copper andacid concentration of the liquid, the amount of sulfide minerals in thefeed slurry and the pulp density of the feed slurry, as well as otherparameters of the pressure leaching process. In an exemplary aspect ofthis embodiment of the invention, a sufficient amount of cooling liquidis added to the pressure leaching vessel to yield a solids content inproduct stream 108 on the order of less than about 50% solids by weight,more preferably ranging from about 3 to about 35% solids by weight, andmost preferably ranging from about 6 to about 15% solids by weight. Inaccordance with one embodiment of the invention, the cooling liquid isadded as lean electrolyte, which effectively controls the acid, iron andcopper concentrations in the discharge slurry.

In accordance with an exemplary aspect of the present invention,pressure leaching of stream 103 is performed in the presence of adispersing agent 126. Suitable dispersing agents useful in accordancewith this aspect of the present invention include, for example, organiccompounds such as lignin derivatives, such as, for example, calcium andsodium lignosulfonates, tannin compounds, such as, for example,quebracho, orthophenylene diamine (OPD), alkyl sulfonates, such as, forexample, sodium alkylbenzene sulfonates, and combinations of the above.Dispersing agent 126 may be any compound that resists degradation in thetemperature range of medium temperature pressure leaching (i.e., fromabout 140° C. to about 180° C.) long enough to disperse the elementalsulfur produced during the medium temperature pressure leaching processand that achieves the desired result of preventing elemental sulfur frompassivating copper values, which may reduce copper extraction.Dispersing agent 126 may be introduced to the pressure leaching vesselin an amount and/or at a concentration sufficient to achieve the desiredresult. In one aspect of an exemplary embodiment of the invention,favorable results are achievable during pressure leaching ofchalcopyrite using calcium lignosulfonate in an amount of about 2 toabout 20 kilograms per tonne, and more preferably in an amount of about4 to about 12 kilograms per tonne; and more preferably in an amount ofabout 6 to about 10 kilograms per tonne of chalcopyrite concentrate.

In accordance with another exemplary embodiment of the presentinvention, a seeding agent may be introduced into reactive processingstep 1030. A suitable seeding agent may comprise any material capable offorming a nucleation site for the crystallization and/or growth of solidspecies. Accordingly, the seeding agent may be any particle which actsas a site for particle accumulation and/or precipitation, and mayoriginate from recycled materials from other stages of the metalrecovery process or may be provided by the addition of substances thatare foreign to the metal recovery process. In some cases, the seedingagent comprises any material that promotes crystallization,precipitation, and/or growth of unwanted materials—for example in thepreferred case of copper recovery, hematite, gangue, and the like—thatmay otherwise tend to partially or completely encapsulate the desiredmetal values, rendering the desired metal values (e.g., copper and gold)generally unavailable or less accessible to a lixiviant solution.

One source of suitable seeding agents useful in accordance with anaspect of this exemplary embodiment are those materials which can befound in the pressure leaching vessel discharge, which materials may berecycled for seeding purposes. Use of the recycled pressure leachingvessel discharge may be desirable for economic reasons, and using aseeding agent that is similar or identical to unwanted particles in thepressure leaching process slurry may tend to encourage the accumulationof unwanted material. For example, in metal recovery processes where anunwanted material, such as hematite, is either present in themetal-bearing material or is produced as a by-product, introduction ofrecycled hematite-containing residue from previous pressure leachingprocesses likely will tend to provide newly formed or liberated hematitea preferential nucleation site. In the absence of this nucleation site,unreactive particles may occlude the desired metal values tosolubilization by precipitating on the surface of the metal values,rendering the metal values unrecoverable. Therefore, introducing aseeding agent to prevent such occlusion may assist in providing bettermetal recovery. In accordance with the exemplary embodiment illustratedin FIG. 1, a portion of the solid residue stream 110 from solid-liquidseparation step 1040 provides a suitable seeding material to reactiveprocessing step 1030.

Subsequent to metal-bearing material stream 103 undergoing reactiveprocessing step 1030, the copper and/or other metal values that havebeen made available by the reactive process undergo one or more ofvarious metal recovery processes. Referring again to FIG. 1, metalrecovery process 1070 (discussed hereinbelow) is a process forrecovering copper and/or other metal values, and may include any numberof preparatory or conditioning steps. For example, a copper-bearingsolution may be prepared and conditioned for metal recovery through oneor more chemical and/or physical processing steps. The product streamfrom reactive processing step 1030 may be conditioned to adjust thecomposition, component concentrations, solids content, volume,temperature, pressure, and/or other physical and/or chemical parametersto desired values and thus to form a suitable copper-bearing solution.Generally, a properly conditioned copper-bearing solution will contain arelatively high concentration of soluble copper in, for example, an acidsulfate solution, and preferably will contain few impurities. Inaccordance with one aspect of an exemplary embodiment of the invention,however, impurities in the conditioned copper-bearing solutionultimately may be decreased through the use of a separatesolvent/solution extraction stage and discussed in connection with theembodiment illustrated in FIG. 2. Moreover, the conditions of thecopper-bearing solution preferably are kept substantially constant toenhance the quality and uniformity of the copper product ultimatelyrecovered.

In one aspect of an exemplary embodiment of the present invention,conditioning of a metal-bearing solution for copper recovery in anelectrowinning circuit begins by adjusting certain physical parametersof the product slurry from the reactive processing step. In an exemplaryaspect of this embodiment of the invention, it may be desirable toreduce the temperature and pressure of the product slurry toapproximately ambient conditions. An exemplary method of so adjustingthe temperature and pressure characteristics of the metal-bearingproduct slurry from a medium temperature pressure leaching stage isatmospheric flashing (such as atmospheric flashing stage 1035 shown inFIG. 1). Further, flashed gases, solids, solutions, and steam mayoptionally be suitably treated, for example, by use of a venturiscrubber wherein water may be recovered and hazardous materials may beprevented from entering the environment.

In accordance with further aspects of this preferred embodiment, afterthe product slurry has been subjected to atmospheric flashing using, forexample, a flash tank, to achieve approximately ambient conditions ofpressure and temperature, the product slurry may be further conditionedin preparation for later metal-value recovery steps. For example, one ormore solid-liquid phase separation stages (such as solid-liquidseparation stage 1040 illustrated in FIG. 1) may be used to separatesolubilized metal solution from solid particles. This may beaccomplished in any conventional manner, including use of filtrationsystems, counter-current decantation (CCD) circuits, thickeners, and thelike. As illustrated in FIG. 1, in accordance with one embodiment of theinvention, conditioning of the product slurry for metal recoverycomprises a solid-liquid separation step 1040 and an optionalelectrolyte treatment step 1050, which further conditions product liquid111 such as, for example, through filtration, to remove fine solidparticles and colloidal matter, such as, for example, silica and/orsilica-bearing material. A variety of factors, such as the processmaterial balance, environmental regulations, residue composition,economic considerations, and the like, may affect the decision whetherto employ a CCD circuit, one thickener or multiple thickeners, onefilter or multiple filters, and/or any other suitable device orcombination of devices in a solid-liquid separation apparatus. However,it should be appreciated that any technique of conditioning the productslurry for later metal value recovery is within the scope of the presentinvention.

As further discussed hereinbelow, the separated solids may further besubjected to later processing steps, including precious metal or othermetal value recovery, such as, for example, recovery of gold, silver,platinum group metals, molybdenum, zinc, nickel, cobalt, uranium,rhenium, rare earth metals, and the like, by cyanidation or othertechniques. Later processing steps may also include treatment processesto remove or recover other mineral constituents from the separatedsolids. Alternatively, the separated solids may be subject toimpoundment or disposal, or, as noted hereinabove, a portion of theseparated solids may be introduced into the reactive processing stage asa seeding agent.

Thus, in accordance with an exemplary aspect of the embodimentillustrated in FIG. 1, product slurry 107 from reactive processing step1030 is subjected to atmospheric flashing 1035 in one or moreatmospheric flash tanks or any other suitable atmospheric system torelease pressure and to evaporatively cool the product slurry 107through the release of steam to form a flashed product slurry 108. Theflashed product slurry preferably has a temperature ranging from about90° C. to about 101° C., a copper concentration of from about 40 toabout 120 grams/liter, and an acid concentration of from about 16 toabout 50 grams/liter. In accordance with an aspect of an exemplaryembodiment of the invention, a portion of flashed product slurry 108(stream 123 in FIG. 1), is recycled to pressure leaching stage 1030.

Flashed product slurry 108 also may contain a particulate solid residuecontaining, for example, the iron oxide by-product of pressure leaching,elemental sulfur and other by-products, precious metals and othercomponents that are undesirable for a feed stream to an electrowinningcircuit. Thus, in accordance with the same principles discussed above,it may be desirable to subject the flashed product slurry to asolid-liquid separation process, such that the liquid portion of theslurry—the desired copper-containing solution—is separated from thesolid portion of the slurry—the undesired residue.

Referring still to FIG. 1, in the illustrated embodiment of theinvention, flashed product slurry 108 is directed to a solid-liquidseparation stage 1040, such as a CCD circuit. In an alternativeembodiment of the invention, solid-liquid separation stage 1040 maycomprise, for example, a thickener or one or more filters. In one aspectof an exemplary embodiment of the invention, a CCD circuit usesconventional countercurrent washing of the residue stream with washwater 109 to recover leached copper to the copper-containing solutionproduct and to minimize the amount of soluble copper advancing to eitherprecious metal recovery processes or residue disposal. Preferably, largewash ratios and/or several CCD stages are utilized to enhance theeffectiveness of solid-liquid separation stage 1040—that is, relativelylarge amounts of wash water 109 are added to the residue in the CCDcircuit and/or several CCD stages are used. Preferably, the solutionportion of the residue slurry stream is diluted by wash water 109 in theCCD circuit to a copper concentration of from about 5 to about 200 partsper million (ppm) in the solution portion of residue stream I 10. Inaccordance with another aspect of an exemplary embodiment of theinvention, addition of a chemical reagent to liquid/solid separationstage 1040 may be desirable to remove deleterious constituents from theprocess stream. For example, a polyethylene oxide may be added toeffectuate removal of silica by precipitation, or other flocculantsand/or coagulants might be utilized to remove other undesirable speciesfrom the process stream. One such suitable chemical reagent is POLYOX™WSR-301, available from Dow Chemical.

Depending on its composition, residue stream 110 from liquid/solidseparation stage 1040 may be neutralized, impounded, disposed of, orsubjected to further processing, such as, for example, precious metalrecovery, treatment to recover other metal values, treatment toattenuate or remediate metals of concern, or other treatment to recoveror remove other mineral constituents from the stream. For example, ifresidue stream 110 contains economically significant amounts of gold,silver, and/or other precious metals, it may be desirable to recoverthis gold fraction through a cyanidation process or other suitablerecovery process. If gold or other precious metals are to be recoveredfrom residue stream 110 by cyanidation techniques, the content ofcontaminants in the stream, such as elemental sulfur, amorphous ironprecipitates, unreacted copper minerals and dissolved copper, ispreferably minimized. Such materials may promote high reagentconsumption in the cyanidation process and thus increase the expense ofthe precious metal recovery operation. As mentioned above, it istherefore preferable to use a large amount of wash water or otherdiluent or several stages during the solid-liquid separation process tomaintain low copper and acid levels in the solids-containing residuestream in an attempt to optimize the conditions for subsequent preciousmetal recovery.

Optionally, as illustrated in FIG. 1 as an aspect of one exemplaryembodiment of the invention, one or more additional electrolytetreatment stages 1050 may be utilized to further condition and/or refineprocess stream 111 from solid-liquid separation stage 1040, such as, forexample, through filtration, thickening, counter-current decantation, orthe like. Moreover, a portion of process stream 111 (stream 122 inFIG. 1) may be recycled to pressure leaching stage 1030, either directlyor through combination with lean electrolyte recycle stream 119 (asshown) and/or other suitable process streams entering the pressureleaching operation. In accordance with an exemplary embodiment, residuestream 114 from electrolyte treatment stage 1050 is subjected to furthertreatment 1080, wherein, depending on the conditions of residue stream114, all or a portion of the stream may be neutralized, impounded,disposed of, or subjected to further processing as described above.Copper-containing solution stream 113 from electrolyte treatment stage1050 is then preferably subjected to copper recovery; however, a portionof copper-containing solution stream 113 (stream 120 in FIG. 1) may berecycled to pressure leaching stage 1030.

Referring again to FIG. 1, in accordance with one aspect of anembodiment of the invention, copper-containing solution stream 113 fromelectrolyte treatment stage 1050 is sent to an electrolyte recycle tank1060. Electrolyte recycle tank 1060 suitably facilitates process controlfor electrowinning circuit 1070, as will be discussed in greater detailbelow. Copper-containing solution stream 113, is preferably blended witha lean electrolyte stream 121 in electrolyte recycle tank 1060 at aratio suitable to yield a product stream 115, the conditions of whichmay be chosen to optimize the resultant product of electrowinningcircuit 1070.

With continued reference to FIG. 1, copper from the product stream 115is suitably electrowon to yield a pure, cathode copper product (stream116 ). In accordance with the various aspects of the invention, aprocess is provided wherein, upon proper conditioning of acopper-containing solution, a high quality, uniformly-plated cathodecopper product 116 may be realized without subjecting thecopper-containing solution to a solvent/solution extraction processprior to entering the electrowinning circuit.

As those skilled in the art are aware, a variety of methods andapparatus are available for the electrowinning of copper and other metalvalues, any of which may be suitable for use in accordance with thepresent invention, provided the requisite process parameters for thechosen method or apparatus are satisfied. For the sake of convenienceand a broad understanding of the present invention, an electrowinningcircuit useful in connection with various embodiments of the inventionmay comprise an electrowinning circuit, constructed and configured tooperate in a conventional manner. The electrowinning circuit may includeelectrowinning cells constructed as elongated rectangular tankscontaining suspended parallel flat cathodes of copper alternating withflat anodes of lead alloy, arranged perpendicular to the long axis ofthe tank. A copper-bearing leach solution may be provided to the tank,for example at one end, to flow perpendicular (referring to the overallflow pattern) to the plane of the parallel anodes and cathodes, andcopper can be deposited at the cathode and water electrolyzed to formoxygen and protons at the anode with the application of current. Otherelectrolyte distribution and flow profiles may be used.

The primary electrochemical reactions for electrowinning of copper fromacid solution is believed to be as follows:2CuSO₄+2H₂O→2Cu°+2H₂SO₄+O₂Cathode half-reaction: Cu²⁺+2e⁻→Cu°Anode half-reaction: 2H₂O→4H⁺+O₂+4e⁻

Turning again to FIG. 1, in a preferred embodiment of the invention,product stream 115 is directed from electrolyte recycle tank 1060 to anelectrowinning circuit 1070, which contains one or more conventionalelectrowinning cells. It should be understood, however, that any methodand/or apparatus currently known or hereinafter devised suitable for theelectrowinning of copper from acid solution, in accordance with theabove-referenced reactions or otherwise, is within the scope of thepresent invention.

In accordance with a preferred aspect of the invention, electrowinningcircuit 1070 yields a cathode copper product 116, optionally, an offgasstream (not shown), and a relatively large volume of copper-containingacid solution, herein designated as lean electrolyte stream 117. Asdiscussed above, in the illustrated embodiment of the invention, aportion of lean electrolyte stream 117 (lean electrolyte recycle stream119 in FIG. 1) is preferably recycled to pressure leaching stage 1030and/or to electrolyte recycle tank 1060. Optionally, a portion ofcopper-containing solution stream 113 (stream 120 in FIG. 1) fromelectrolyte treatment stage 1050 is combined with lean electrolyterecycle stream 119 and is recycled to pressure leaching stage 1030.Moreover, in accordance with one aspect of an exemplary embodiment ofthe invention, a portion of lean electrolyte stream 117 (leanelectrolyte bleed stream 118 in FIG. 1) is removed from process 100 forthe removal of impurities and acid and/or residual copper recoveryoperations, such as, for example, those illustrated in FIG. 2.

Preferably, lean electrolyte recycle stream 119 comprises at least about50 percent by weight of lean electrolyte stream 117, more preferablyfrom about 60 to about 95 percent by weight of lean electrolyte stream117, and more preferably from about 80 to about 90 percent by weight oflean electrolyte stream 117. Preferably, lean electrolyte bleed stream118 comprises less than about 50 percent by weight of lean electrolytestream 118, more preferably from about 5 to about 40 percent by weightof lean electrolyte stream 117, and more preferably from about 10 toabout 20 percent by weight of lean electrolyte stream 117.

Copper values from the metal-bearing product stream 115 are removedduring electrowinning step 1070 to yield a pure, cathode copper product.It should be appreciated that in accordance with the various aspects ofthe invention, a process wherein, upon proper conditioning of themetal-bearing solution, a high quality, uniformly-plated cathode copperproduct may be realized without subjecting the metal-bearing solution tosolvent/solution extraction prior to entering the electrowinning circuitis within the scope of the present invention. As previously noted,careful control of the conditions of the metal-bearing solution enteringan electrowinning circuit—especially maintenance of a substantiallyconstant copper composition in the stream—can enhance the quality of theelectrowon copper by, among other things, enabling even plating ofcopper on the cathode and avoidance of surface porosity in the cathodecopper, which degrades the copper product and thus may diminish itseconomic value. In accordance with this aspect of the invention, suchprocess control can be accomplished using any of a variety of techniquesand equipment configurations, so long as the chosen system and/or methodmaintains a sufficiently constant feed stream to the electrowinningcircuit. As those skilled in the art are aware, a variety of methods andapparatus are available for the electrowinning of copper and other metalvalues, any of which may be suitable for use in accordance with thepresent invention, provided the requisite process parameters for thechosen method or apparatus are satisfied.

In accordance with an exemplary embodiment of the invention illustratedin FIG. 2, lean electrolyte bleed stream 118 from electrowinning unit1070 (FIG. 1) is sent to a solvent/solution extraction stage 2010. Inaccordance with one embodiment of the invention, solvent/solutionextraction stage 2010 is configured to treat materials from atmosphericand/or pressure leach operations 2020 as well as lean electrolyte bleedstream 118. Leach operation 2020 may utilize any conventional orhereinafter developed atmospheric or pressure leaching method,including, for example, heap leaching, stockpile leaching (alsosometimes referred to in the art as “dump leaching”), vat leaching, tankleaching, agitated tank leaching, in situ leaching, pressure leaching,or other process. In accordance with one aspect of a preferredembodiment of the invention, leach operation 2020 is a conventionalacid-consuming heap leach operation, wherein a low grade ore 201 iscontacted with an acid-containing stream 202 and, optionally, otherprocess streams, such as raffinate stream 205 from solvent/solutionextraction unit 2010. In leach operation 2020, the acid percolatesdownward through the ore heap, solubilizing the copper in thecopper-containing ore in the form of copper sulfate, to form acopper-rich pregnant leach solution (PLS) stream 203. In accordance withone aspect of a preferred embodiment of the invention, PLS 203 from aheap leach operation 2020 is combined with lean electrolyte bleed stream118 prior to entering solvent/solution extraction stage 2010 as processstream 204.

In accordance with a further aspect of this embodiment of the presentinvention, as previously briefly mentioned, lean electrolyte bleedstream 118 advantageously may remove impurities from the process, forexample the electrowinning process. Such impurities include, withoutlimitation, iron, aluminum, silica, selenium, magnesium, manganese,sodium, potassium and others. In the absence of removal, such impuritiesmay accumulate to deleterious levels, and, as such negatively impactproduction efficiencies and product (e.g., copper cathode) quality. Thepresence of such impurities in lean electrolyte bleed stream 118generally does not negatively impact the aforementioned handling of leanelectrolyte bleed stream 118.

As will be discussed in further detail hereinbelow, in a furtherembodiment of the present invention, impurities may be removed prior topressure leaching through any suitable means, such as precipitation orother steps.

With further reference to FIG. 2, solvent/solution extraction stage 2010and solution stripping stage 2015 purify copper-bearing process stream204 in two unit operations—an extraction operation, which may havemultiple stages, followed by a stripping operation. In the extractionstage, process stream 204 is contacted with an organic phase consistingof a diluent in which a copper selective reagent (i.e., the extractant)is admixed. When the solutions are contacted, the organic extractantchemically removes the copper from stream 204, forming a copper-depletedaqueous raffinate stream. The raffinate and organic streams aresubsequently separated in a settler. After separation of the organic andaqueous phases in the settler, a portion of the aqueous phase (stream205) is typically returned to one or more leaching operations to bereloaded with copper from the ore in the atmospheric leach to form thePLS, or may be recycled to other process areas or appropriately disposedof. The organic stream passes on to the second unit operation of thesolvent/solution extraction process, the stripping operation. In thestripping operation, the organic stream is contacted with a stronglyacidic electrolyte. This acidic solution “strips” the copper from theextractant, leaving the organic phase substantially depleted of copper.At least a portion of the loaded strip solution aqueous phase (stream206) is advanced to an electrowinning plant 2030 as a copper “rich”solution. Aqueous stream 206 is processed in electrowinning plant 2030to yield cathode copper 207 and a copper-containing lean electrolytestream 208, which, in one aspect of a preferred embodiment of theinvention, may be recycled in part to solvent/solution extraction unit2010 and/or to pressure leaching stage 1030 (stream 209 to FIG. 1)and/or to other process areas.

In accordance with one alternative aspect of the invention, aqueousstream 206 may not be subjected to electrowinning immediately afterleaving the solvent/solution extraction unit, but may instead be blendedwith other copper-containing process streams, and the resultant streamthen sent to an electrowinning circuit. For example, all or a portion ofaqueous stream 206 may be blended with a copper-containing solutionstream (not shown) and a lean electrolyte stream (not shown) inelectrolyte recycle tank 1060 (from FIG. 1) to form a resultant productstream suitable for electrowinning in an electrowinning circuit. In suchcases the stripping solutions used in solvent/solution extraction 2010likely will be comprised of spent electrolyte from electrowinningcircuit 1070 (from FIG. 1).

Impurity removal may be further facilitated by suitable processing inadvance of pressure leaching, such as by the aforementioned separationand/or precipitation step. In accordance with this further aspect of thepresent invention as previously mentioned, advantageously impurities maybe removed from the process, for example, the electrowinning process.Such impurities include, without limitation, iron, aluminum, magnesium,sodium, potassium and the like, often present as sulfates. In theabsence of removal, such impurities may accumulate to deleteriouslevels, and, as such negatively impact production efficiencies andproduct (e.g. copper cathode) quality.

The Example set forth hereinbelow is illustrative of various aspects ofa preferred embodiment of the present invention. The process conditionsand parameters reflected therein are intended to exemplify variousaspects of the invention, and are not intended to limit the scope of theclaimed invention.

EXAMPLE 1

Copper was recovered from chalcopyrite-containing concentrate usingcontinuous medium temperature pressure leaching and directelectrowinning in accordance with an exemplary embodiment of theinvention. Table 1, below, sets forth the process conditions andoperating parameters utilized.

TABLE 1 FEED Concentrate Type Chalcopyrite Concentrate Analyses, % Cu31.6 Fe 30.5 S 34.2 Grind Size. P₉₈, μm 15 PRESSURE LEACHINGTemperature, ° C. 160 Time, min 90 Acid Addition Rate, kg acid/tonnefeed 450 CLS Addition Rate, kg CLS/tonne feed 10 Oxygen Overpressure,psi 200 Total Pressure, psi 290 Feed Solids to Compartment 1, % 10.3Weight Loss, % 20 Discharge Solids, % 7.4 Discharge Solution, g/L Cu 102Fe 4.6 H₂SO₄ 11.6 Discharge Solids, % Cu 1.5 Fe 35.9 Cu Extraction, %96.6 Sulfide Oxidized to Elemental Sulfur, % 69 Sulfide Oxidation toSulfate, % 27 ELECTROWINNING Current Density, A/m² 308 Cell Temperature,° C. 50 Specific Flow, L/min-m2 3.0 FC-1110 (Mist Control), gal/10⁶ lbCu 10 PD-4201 (Leveling Agent), g/tonne Cu 334 Lean Electrolyte, g/L Cu34 Fe 3.3 H₂SO₄ 135 Current Efficiency, % 88 Copper Removed byElectrowinning, % 84

An effective and efficient method to recover copper from metal-bearingmaterials, especially copper from copper sulfides, such as chalcopyrite,that enables high copper recovery at a reduced cost over conventionalprocessing techniques has been presented herein. In accordance with thepresent invention, it has been shown that copper recovery in excess ofabout 96 to about 98 percent is achievable while realizing variousimportant economic benefits of medium temperature pressure leaching andcircumventing processing problems historically associated with mediumtemperature pressure leaching. Moreover, the present invention providesa substantially acid-autogenous process for recovering copper fromchalcopyrite-containing ore using pressure leaching and directelectrowinning in combination with an atmospheric leaching,solvent/solution extraction, and electrowinning steps.

The present invention has been described above with reference to anumber of exemplary embodiments and examples. It should be appreciatedthat the particular embodiments shown and described herein areillustrative of the invention and its best mode and are not intended tolimit in any way the scope of the invention. Those skilled in the arthaving read this disclosure will recognize that changes andmodifications may be made to the exemplary embodiments without departingfrom the scope of the present invention. Further, although certainpreferred aspects of the invention are described herein in terms ofexemplary embodiments, such aspects of the invention may be achievedthrough any number of suitable means now known or hereafter devised.Accordingly, these and other changes or modifications are intended to beincluded within the scope of the present invention.

1. A method of recovering copper from a copper-bearing material, comprising the steps of: (a) providing a feed stream comprising a copper-bearing material; (b) subjecting at least a portion of said feed stream to controlled fine grinding; (c) leaching at least a portion of said inlet stream in an oxidizing environment at an elevated temperature and pressure to yield a product slurry comprising a copper-bearing solution and a residue; (d) conditioning said product slurry without the use of solvent/solution extraction techniques to yield a copper-bearing solution suitable for electrowinning; (e) electrowinning copper from said copper-bearing solution to yield cathode copper and a copper-bearing lean electrolyte stream; (f) recycling a portion of said lean electrolyte stream to said leaching stage; and (g) treating at least a portion of said lean electrolyte stream using solvent/solution extraction techniques.
 2. The method of claim 1, wherein said step of providing a feed stream comprising a copper-bearing material comprises providing a feed stream comprising a copper-bearing sulfide ore, concentrate, or precipitate.
 3. The method of claim 1, wherein said step of providing a feed stream comprising a copper-bearing material comprises providing a feed stream comprising at least one of chalcopyrite, chalcocite, bornite, covellite, digenite, and enargite, or mixtures or combinations thereof.
 4. The method of claim 1, wherein said step of providing a feed stream comprising a copper-bearing material comprises providing a feed stream comprising a copper-bearing material and a solution stream comprising copper and acid.
 5. The method of claim 1, wherein said step of subjecting at least a portion of said feed stream to controlled fine grinding comprises reducing the particle size of said feed stream such that substantially all of the particles in said feed stream react substantially completely during pressure leaching.
 6. The method of claim 5, wherein said step of subjecting at least a portion of said feed stream to controlled fine grinding comprises reducing the particle size of said feed stream to a P80 of less than about 25 microns.
 7. The method of claim 5, wherein said step of subjecting at least a portion of said feed stream to controlled fine grinding comprises reducing the particle size of said feed stream to a P80 of from about 13 to about 20 microns.
 8. The method of claim 5, wherein said step of subjecting at least a portion of said feed stream to controlled fine grinding comprises reducing the particle size of said feed stream to a P98 of less than about 25 microns.
 9. The method of claim 5, wherein said step of subjecting at least a portion of said feed stream to controlled fine grinding comprises reducing the particle size of said feed stream to a P98 of from about 10 to about 23 microns.
 10. The method of claim 5, wherein said step of subjecting at least a portion of said feed stream to controlled fine grinding comprises reducing the particle size of said feed stream to a P98 of from about 13 to about 15 microns.
 11. The method of claim 1, wherein said leaching step comprises leaching at least a portion of said feed stream in a pressure leaching vessel at a temperature of from about 140° C. to about 230° C. and at a total operating pressure of from about 100 psi to about 750 psi.
 12. The method of claim 1, wherein said leaching step comprises leaching at least a portion of said feed stream in a pressure leaching vessel at a temperature of from about 160° C. to about 170° C. and at a total operating pressure of from about 100 psi to about 750 psi.
 13. The method of claim 1, wherein said leaching step comprises leaching at least a portion of said feed stream in a pressure leaching vessel at a temperature of from about 180° C. to about 220° C. and at a total operating pressure of from about 100 psi to about 750 psi.
 14. The method of claim 1, wherein said step of pressure leaching said feed stream comprises pressure leaching said feed stream in the presence of a surfactant selected from the group consisting of lignin derivatives, orthophenylene diamine, alkyl sulfonates, and mixtures thereof.
 15. The method of claim 1, wherein said conditioning step comprises subjecting at least a portion of said product slurry to solid-liquid separation, wherein at least a portion of said copper-bearing solution is separated from said residue.
 16. The method of claim 15, wherein said conditioning step further comprises blending at least a portion of said copper-bearing solution with at least a portion of one or more copper-bearing streams to achieve a copper concentration of from about 15 grams/liter to about 80 grams/liter in said copper-bearing solution.
 17. The method of claim 15, wherein a portion of said copper-bearing solution is recycled to step (c).
 18. The method of claim 1, wherein said conditioning step comprises subjecting at least a portion of said product slurry to filtration, wherein at least a portion of said copper-bearing solution is separated from said residue.
 19. The method of claim 1, wherein said conditioning step comprises separating at least a portion of said residue from said copper-bearing solution in said product slurry, and further comprises using at least a portion of said residue as a seeding agent in step (c).
 20. The method of claim 1, further comprising the step of (h) using a portion of said lean electrolyte stream in a leaching operation. 